Imaging 101

It travels slightly slower in normal air but it is still written as 300,000,000 m/s for rounding reasons.

In a single medium with a uniform density light will travel in a straight line at the same speed.

Light changes direction when it reflects or refracts.

Specular reflection is when there is an even surface and all the light gets reflected in the same direction. When any reflection occurs the angle of incidence is equal to the angle of reflection.

Diffuse reflection is when there is a microscopically rough surface and this does not reflect back light uniformly. it is why you can get matt finishes. When diffuse reflection happens light is reflected in every direction.